A particulate filter is often used to filter a particulate from an exhaust gas, such as a diesel exhaust gas. As the diesel exhaust gas passes through the filter, the filter removes a soot particulate from the exhaust gas. In this way, the diesel exhaust gas is scrubbed by the filter.
As the filter collects the soot particulate, the filter becomes saturated with the soot particulate. The soot builds-up to the point where it clogs the filter, creates back pressure, and reduces engine efficiency. Further, the effectiveness of the filter decreases. To restore the effectiveness of the filter, and the engine to peak efficiency, the filter must be regenerated by removing soot particles from the filter. After regeneration, the filter can then effectively remove additional soot particles from the diesel exhaust, and may be regenerated again after the filter becomes resaturated.
In one technique, a particulate filter is thermally regenerated by heating the soot particulate in the filter to a combustion temperature. The soot particulate combusts in the filter and is expelled from the filter by the exhaust gas. This technique, however, requires heating the entire soot particulate in the filter to the combustion temperature, which may consume large amounts of energy.
Thermal regeneration of diesel particulate filters requires a considerably higher temperature than normally encountered in diesel exhaust. Although the temperature of diesel exhaust is typically in the range of 150 to 250 degrees centigrade, a temperature of 550 to 750 degrees centigrade is required to create a self-propagating thermal regeneration of a diesel particulate in a diesel particulate filter. Consequently, to achieve thermal regeneration, the temperature of the diesel exhaust, the diesel particulate filter, or a diesel particulate must be increased.
Known methods of heating the exhaust gas temperature include the use of electric heaters and fuel burners, and the injection of combustibles and catalysts into the exhaust system. These methods are used in active filter systems and include a general cycle consisting of a sustained particulate accumulation time followed by a short high temperature regeneration period. While often successful, many of the methods have been shown to have adverse effects on either the diesel particulate filter or the operation of an engine in a vehicle including the diesel particulate filter. Specifically, these methods may result in filter cracking and destruction due to thermal gradients, increased fuel consumption, lower oxygen concentration in the diesel exhaust, and higher intrinsic particulate or hydrocarbon emissions in the diesel exhaust.
In light of the above, there exists a need for an energy efficient regenerating particulate filter.